The Loess Plateau region in China is characterized by a fragile environment,where vegetation is susceptible to both natural variations and anthropogenic influences.Previous research has indicated a greening trend in v...The Loess Plateau region in China is characterized by a fragile environment,where vegetation is susceptible to both natural variations and anthropogenic influences.Previous research has indicated a greening trend in vegetation across the Loess Plateau over the past two decades.However,the specific contributions of natural and anthropogenic drivers,both individually and interactively,to vegetation distribution remain unclear.To address this gap,we conducted a study using Shaanxi Province as a case area.Utilizing multisource data,we employed the Geographical Detector Model(GDM)to analyze the impacts of natural and human related factors on vegetation distribution.Our analysis revealed that the average NDVI(Normalized Difference Vegetation Index)increased at a rate of 0.006 per year from 2000 to 2021.Notably,88.8%of the region experienced vegetation greening,while 4.5%showed significant declines in NDVI,particularly in areas,such as Xi'an,Weinan,Baoji,Hanzhong,and Ankang.Furthermore,NDVI trend projections suggest that the area undergoing vegetation degradation may surpass the area showing improvement in the future.The study identified that vegetation distribution was influenced by both natural and anthropogenic factors for the whole study area.Precipitation,surface types and land use type were the primary factors with q values above 0.5.During the study period,impacts of GDP,nighttime lights and population density among anthropogenic factors on vegetation distribution increased by 130%,125%and 41%,respectively.Conversely,except for slope and aspect,natural factors'influence on vegetation distribution declined by 5%to 26%.The impact of driving factors on NDVI distribution varied across ecological regions.In Fenwei Basin Agro-Ecoregion(EcoregionⅢ),the influence of anthropogenic factors on vegetation distribution was greater than that in the other three ecoregions.Precipitation primarily affected the vegetation distribution in Loess Plateau Agricultural and Grassland Ecoregion(EcoregionⅡ).Additionally,the combined interactive effects of factors had a stronger influence on NDVI distribution than any single factor.These findings provide valuable insights for local governments in Shaanxi Province to develop targeted ecological restoration and environmental management policies.展开更多
In this study, two-dimensional MXene (Ti3 C2 Tx ) was employed to modify the interface of carbon fiber-reinforced polyetherketoneketone (CF/PEKK) composites, in order to simultaneously improve the electromagnetic inte...In this study, two-dimensional MXene (Ti3 C2 Tx ) was employed to modify the interface of carbon fiber-reinforced polyetherketoneketone (CF/PEKK) composites, in order to simultaneously improve the electromagnetic interference (EMI) shielding performances and mechanical properties. The obtained CF/PEKK composites possessed outstanding EMI and mechanical performances, as anticipated. Specifically, the CF/PEKK composites modified with MXene at 1 mg mL–1 exhibited an excellent EMI shielding effectiveness of 65.2 dB in the X-band, a 103.1% enhancement compared with the unmodified CF/PEKK composites. The attractive EMI shielding performances of CF/PEKK composites originated from enhanced ohmic losses and multiple reflections of electromagnetic waves with the help of the MXene and CF layers. In addition, CF/PEKK composites achieved the best mechanical properties by optimizing the dispersion concentration of MXene to 0.1 mg mL–1 . The flexural strength, flexural modulus, and interlaminar shear strength of CF/PEKK composites reached 1127 MPa, 81 GPa, and 89 MPa, which were 28.5%, 9.5%, and 29.7% higher than that of the unmodified CF/PEKK composites, respectively. Such improvement in mechanical properties could be ascribed to the comprehensive effect of mechanical interlocking, hydrogen bonds, and Van der Waals forces between the introduced MXene and CF, PEKK, respectively.展开更多
目的比较不同剂量阿芬太尼对老年患者快速顺序诱导气管插管心血管反应的影响。方法选择2022年3—9月行气管插管全麻老年患者96例,男47例,女49例,年龄65~80岁,BMI 18~24 kg/m^(2),ASAⅠ或Ⅱ级。采用随机数字表法分为四组:阿芬太尼10μg/k...目的比较不同剂量阿芬太尼对老年患者快速顺序诱导气管插管心血管反应的影响。方法选择2022年3—9月行气管插管全麻老年患者96例,男47例,女49例,年龄65~80岁,BMI 18~24 kg/m^(2),ASAⅠ或Ⅱ级。采用随机数字表法分为四组:阿芬太尼10μg/kg组(A组)、阿芬太尼15μg/kg组(B组)、阿芬太尼20μg/kg组(C组)和阿芬太尼25μg/kg组(D组),每组24例。记录麻醉诱导前、气管插管后1、5 min的HR、MAP,同时抽取患者静脉血3 ml,检测血浆中去甲肾上腺素(NE)和皮质醇(Cor)的浓度、超声测量心脏指数(CI)、心脏射血分数(EF)。记录麻醉诱导后至气管插管后5 min高血压、低血压、心动过缓、心动过速的发生情况。结果与麻醉诱导前比较,A组和B组在气管插管后1、5 min HR明显增快,MAP、NE和Cor浓度明显升高,CI和EF明显降低(P<0.05);C组和D组气管插管后1 min HR明显增快,MAP明显升高,D组插管后5 min HR明显减慢,MAP、血浆NE和Cor浓度、CI和EF明显降低(P<0.05)。与A组比较,C组和D组气管插管后1、5 min HR明显减慢,血浆NE和Cor浓度明显降低,气管插管后1 min CI和EF明显升高,高血压和心动过速发生率明显降低(P<0.05);D组插管后5 min CI和EF明显降低,低血压和心动过缓发生率明显升高(P<0.05)。结论阿芬太尼20μg/kg用于老年患者快速顺序诱导气管插管,可有效抑制插管引起的剧烈心血管反应,同时避免心血管系统的抑制,血流动力学更平稳。展开更多
The mechanical behavior of coal is the key factor affecting underground coal mining and coalbed methane extraction.In this study,triaxial compression and seepage tests were carried out on coal at different gas pressur...The mechanical behavior of coal is the key factor affecting underground coal mining and coalbed methane extraction.In this study,triaxial compression and seepage tests were carried out on coal at different gas pressures.The mechanical properties and failure process of coal were studied,as well as the acoustic emission(AE)and strain energy.The influence of gas pressure on the mechanical parameters of this coal was analyzed.Based on the conventional energy calculation formula,the pore pressure was introduced through the effective stress formula,and each energy component of coal containing gas was refined innovatively.The contribution of gas pressure to the total energy input and dissipation during loading was quantitatively described.Finally,the influence of gas pressure on coal strength was theo-retically analyzed from the perspectives of MohreCoulomb criterion and fracture mechanics.The results show that the total absorbed energy comprises the absorbed energy in the axial pressure direction(positive)and in the confining pressure direction(negative),as well as that induced by the pore pressure(initially negative and then positive).The absorbed energy in the axial pressure direction accounts for the main proportion of the total energy absorbed by coal.The quiet period of AE in the initial stage shortens,and AE activity increases during the pre-peak stage under high gas pressure.The fractal characteristics of AE in three stages are studied using the correlation dimension.The AE process has different forms of self-similarity in various deformation stages.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0801304)Philosophy and Social Science Foundation of China(Grant No.23BRK011,24CTJ021)+3 种基金the Humanities and Social Sciences Research Planning Fund of the Ministry of Education,China(Grant No.22YJAZH020)Shaanxi Provincial Social Science Foundation(Grant No.2024D041)Graduate Innovation Funds of Xi’an University of Finance and Economics(Grant No.23YC011)the Youth Innovation Team of Shaanxi Universities,China。
文摘The Loess Plateau region in China is characterized by a fragile environment,where vegetation is susceptible to both natural variations and anthropogenic influences.Previous research has indicated a greening trend in vegetation across the Loess Plateau over the past two decades.However,the specific contributions of natural and anthropogenic drivers,both individually and interactively,to vegetation distribution remain unclear.To address this gap,we conducted a study using Shaanxi Province as a case area.Utilizing multisource data,we employed the Geographical Detector Model(GDM)to analyze the impacts of natural and human related factors on vegetation distribution.Our analysis revealed that the average NDVI(Normalized Difference Vegetation Index)increased at a rate of 0.006 per year from 2000 to 2021.Notably,88.8%of the region experienced vegetation greening,while 4.5%showed significant declines in NDVI,particularly in areas,such as Xi'an,Weinan,Baoji,Hanzhong,and Ankang.Furthermore,NDVI trend projections suggest that the area undergoing vegetation degradation may surpass the area showing improvement in the future.The study identified that vegetation distribution was influenced by both natural and anthropogenic factors for the whole study area.Precipitation,surface types and land use type were the primary factors with q values above 0.5.During the study period,impacts of GDP,nighttime lights and population density among anthropogenic factors on vegetation distribution increased by 130%,125%and 41%,respectively.Conversely,except for slope and aspect,natural factors'influence on vegetation distribution declined by 5%to 26%.The impact of driving factors on NDVI distribution varied across ecological regions.In Fenwei Basin Agro-Ecoregion(EcoregionⅢ),the influence of anthropogenic factors on vegetation distribution was greater than that in the other three ecoregions.Precipitation primarily affected the vegetation distribution in Loess Plateau Agricultural and Grassland Ecoregion(EcoregionⅡ).Additionally,the combined interactive effects of factors had a stronger influence on NDVI distribution than any single factor.These findings provide valuable insights for local governments in Shaanxi Province to develop targeted ecological restoration and environmental management policies.
基金supported by the Shanghai Science and Tech-nology Committee(No.22511102400)Prof.Zhang would like to appreciate the financial support from the Fundamental Research Funds for the Central Universities(No.2232020G-12)+1 种基金the Fund of National Engineering Research Center for Commercial Aircraft Manufacturing(No.COMAC-SFGS-2022-2376)the Textile Vi-sion Basic Research Program(No.J202105).
文摘In this study, two-dimensional MXene (Ti3 C2 Tx ) was employed to modify the interface of carbon fiber-reinforced polyetherketoneketone (CF/PEKK) composites, in order to simultaneously improve the electromagnetic interference (EMI) shielding performances and mechanical properties. The obtained CF/PEKK composites possessed outstanding EMI and mechanical performances, as anticipated. Specifically, the CF/PEKK composites modified with MXene at 1 mg mL–1 exhibited an excellent EMI shielding effectiveness of 65.2 dB in the X-band, a 103.1% enhancement compared with the unmodified CF/PEKK composites. The attractive EMI shielding performances of CF/PEKK composites originated from enhanced ohmic losses and multiple reflections of electromagnetic waves with the help of the MXene and CF layers. In addition, CF/PEKK composites achieved the best mechanical properties by optimizing the dispersion concentration of MXene to 0.1 mg mL–1 . The flexural strength, flexural modulus, and interlaminar shear strength of CF/PEKK composites reached 1127 MPa, 81 GPa, and 89 MPa, which were 28.5%, 9.5%, and 29.7% higher than that of the unmodified CF/PEKK composites, respectively. Such improvement in mechanical properties could be ascribed to the comprehensive effect of mechanical interlocking, hydrogen bonds, and Van der Waals forces between the introduced MXene and CF, PEKK, respectively.
文摘目的比较不同剂量阿芬太尼对老年患者快速顺序诱导气管插管心血管反应的影响。方法选择2022年3—9月行气管插管全麻老年患者96例,男47例,女49例,年龄65~80岁,BMI 18~24 kg/m^(2),ASAⅠ或Ⅱ级。采用随机数字表法分为四组:阿芬太尼10μg/kg组(A组)、阿芬太尼15μg/kg组(B组)、阿芬太尼20μg/kg组(C组)和阿芬太尼25μg/kg组(D组),每组24例。记录麻醉诱导前、气管插管后1、5 min的HR、MAP,同时抽取患者静脉血3 ml,检测血浆中去甲肾上腺素(NE)和皮质醇(Cor)的浓度、超声测量心脏指数(CI)、心脏射血分数(EF)。记录麻醉诱导后至气管插管后5 min高血压、低血压、心动过缓、心动过速的发生情况。结果与麻醉诱导前比较,A组和B组在气管插管后1、5 min HR明显增快,MAP、NE和Cor浓度明显升高,CI和EF明显降低(P<0.05);C组和D组气管插管后1 min HR明显增快,MAP明显升高,D组插管后5 min HR明显减慢,MAP、血浆NE和Cor浓度、CI和EF明显降低(P<0.05)。与A组比较,C组和D组气管插管后1、5 min HR明显减慢,血浆NE和Cor浓度明显降低,气管插管后1 min CI和EF明显升高,高血压和心动过速发生率明显降低(P<0.05);D组插管后5 min CI和EF明显降低,低血压和心动过缓发生率明显升高(P<0.05)。结论阿芬太尼20μg/kg用于老年患者快速顺序诱导气管插管,可有效抑制插管引起的剧烈心血管反应,同时避免心血管系统的抑制,血流动力学更平稳。
基金This study is sponsored by the National Natural Science Foun-dation of China(Grant No.12002270)the China Postdoctoral Science Foundation(Grant Nos.2021T140553 and 2021M692600).
文摘The mechanical behavior of coal is the key factor affecting underground coal mining and coalbed methane extraction.In this study,triaxial compression and seepage tests were carried out on coal at different gas pressures.The mechanical properties and failure process of coal were studied,as well as the acoustic emission(AE)and strain energy.The influence of gas pressure on the mechanical parameters of this coal was analyzed.Based on the conventional energy calculation formula,the pore pressure was introduced through the effective stress formula,and each energy component of coal containing gas was refined innovatively.The contribution of gas pressure to the total energy input and dissipation during loading was quantitatively described.Finally,the influence of gas pressure on coal strength was theo-retically analyzed from the perspectives of MohreCoulomb criterion and fracture mechanics.The results show that the total absorbed energy comprises the absorbed energy in the axial pressure direction(positive)and in the confining pressure direction(negative),as well as that induced by the pore pressure(initially negative and then positive).The absorbed energy in the axial pressure direction accounts for the main proportion of the total energy absorbed by coal.The quiet period of AE in the initial stage shortens,and AE activity increases during the pre-peak stage under high gas pressure.The fractal characteristics of AE in three stages are studied using the correlation dimension.The AE process has different forms of self-similarity in various deformation stages.
